1. Field of the Invention
The present invention relates to a thin film magnetic head in which a coil layer is provided between core layers, and more particularly to a thin film magnetic head in which an excellent non-linear transition shift (hereinafter referred to as NLTS) characteristic and an excellent overwrite (hereinafter referred to as OW) characteristic can be simultaneously obtained.
2. Description of the Related Art
FIG. 8 is an enlarged detail of a conventional thin film magnetic head showing a construction of a facing surface facing a recording medium. FIG. 9 is a longitudinal sectional view of the thin film magnetic head shown in FIG. 8. FIG. 10 is a fragmentary isometric view of an entire construction of the conventional thin film magnetic head.
The thin film magnetic head shown in FIGS. 8 to 10 is a combined-type thin film magnetic head in which a read-out head h1 using a magnetoresistive effect and an inductive magnetic head h2 for writing a signal on a recording medium such as a hard disk are laminated. As shown in FIG. 10, the thin film magnetic head is provided at a trailing side end surface 12a of a slider 12 of a floating type magnetic head.
Reference numeral 20 in FIGS. 8 to 10 indicates a lower core layer which is made of a magnetic material having a high magnetic permeability such as an Fe--Ni based alloy (Permalloy). The lower core layer 20 functions also as an upper shielding layer of the read-out head h1 using a magnetoresistive effect. A gap layer 21 which is made of a nonmagnetic material such as A1.sub.2 O.sub.3 (aluminum oxide) is formed on the lower core layer. As shown in FIG. 9, an insulating layer 22 which is made of organic resin materials including resist materials are provided on the gap layer 21.
Coil layers 23 which are made of an electric conductive material having a low electric resistance such as Cu are helically provided on the insulating layer 22. As shown in FIG. 9, an insulating layer 24 which is made of organic resin materials including resist materials is formed on the coil layers 23. Further, a magnetic material such as Permalloy is plated on the insulating layer 24 to form an upper core layer 25. As shown in FIG. 8, a protective layer 26 is provided on the upper core layer 25.
As shown in FIG. 10, the upper core layer 25 includes a tip portion A having a constant width and a rear end portion B which gradually becomes wider starting from the tip portion A toward the rear end side. As shown in FIG. 9, the tip of the tip portion A is connected with the lower core layer 20 by interposing the gap layer 21 at a facing portion facing onto a recording medium so as to form a magnetic gap having a gap length of G11. In addition, as shown in FIGS. 9 and 10, a base end portion 25a of the upper core layer 25 is magnetically brought into contact with the lower core layer 20 through a groove formed at the gap layer 21 and the insulating layer 22.
With respect to the inductive magnetic head for writing h2, when a recording current is applied to the coil layer 23, a recording magnetic field is induced in the lower core layer 20 and the upper core layer 25. Thus, a magnetic signal is recorded on a recording medium such as a hard disk using a leakage magnetic field from a magnetic gap portion between the tip of the lower core layer 20 and the tip of the upper core layer 25.
In addition, as shown in FIGS. 8 to 10, the read-out head h1 which is provided under the inductive magnetic head h2 comprises a lower shielding layer 30 which is made of a magnetic material, a magnetoresistive device layer 32 which is provided on the lower shielding layer 30 by interposing a lower gap layer 31, and an upper shielding layer 20 (a lower core layer) which is formed on the magnetoresistive device layer 32 by interposing an upper gap layer 33.
When the recording density becomes higher, a leakage magnetic field which arises at a magnetic gap between the core layers 20 and 25 in the inductive magnetic head h2 shown in FIGS. 8 to 10 is affected by a leakage magnetic field which arises in a direction starting from a recording signal immediately recorded on a recording medium to the head side. Thus, nonlinear distortion arises so as to easily induce a phase shift (that is, NLTS). This NLTS characteristic greatly depends on the configuration of the portion A of the upper core layer 25. In addition, an important recording characteristic in addition to the NLTS characteristic is the OW characteristic.
The term "overwrite" means "double write". The OW characteristic is evaluated as follows. A signal is recorded at a low frequency and then another signal is overwritten at a high frequency. The OW characteristic is evaluated by the degree of decrease in a residual output power of the recording signal at a low frequency in the overwritten state compared with that before overwriting at a high frequency.
The OW characteristic also depends on the configuration of the tip portion A of the upper core layer 25 similarly to the NLTS characteristic. Conventionally, the tip portion A has been appropriately configured to be excellent in only one of the NLTS and OW characteristics, and excellent NLTS and OW characteristics cannot be simultaneously obtained.